The present invention relates to a device and a process for regulating the power of the engines of a rotary wing aircraft, in particular a helicopter, which is multi-engine, in particular twin engine.
It is known that such a regulating device comprises main regulating systems associated respectively with said engines of the aircraft and intended to supply fuel to the respective associated engines, in particular so as to maintain, in flight, the speed of rotation of the main forward propulsion and lift rotor at a substantially constant value.
Moreover, backup devices are known which are associated respectively with said main regulating systems and which make it possible, should there be a fault with one of said main regulating systems, to adjust the power delivered by the associated engine in such a way as to satisfy the requirements corresponding to the maneuvers which the aircraft is currently carrying out.
However, these known backup devices are of manual type and require, at each instant, manual adjustment of the flow rate of the fuel on the part of the pilot.
This therefore increases the pilot""s workload. Furthermore, because of the difficulty of adjustment during flight, the pilot requires particular training. Additionally, in particular in order to reduce the risks which could result from insufficient training of the pilot, appropriate means are provided, so that such a backup device is generally very complex and expensive.
The object of the present invention is to remedy these drawbacks. It relates to an especially simple and effective device for regulating the power of the engines of a rotary wing aircraft, in particular a helicopter furnished with at least two engines.
To this end, according to the invention, said regulating device, comprising main regulating systems associated respectively with said engines and intended to supply fuel to the associated engines respectively, is noteworthy in that it furthermore comprises auxiliary regulating systems associated respectively with said engines, and means for determining the speeds of rotation of said engines, and in which each of said auxiliary regulating systems comprises:
at least one triggering means for triggering said auxiliary regulating system, when the main regulating system of the associated engine has failed;
a controllable supply means which is capable of supplying fuel to the associated engine; and
a control means capable of automatically controlling said supply means so as to adjust the fuel flow rate in such a way as to slave the speed of rotation of the engine, whose main regulating system has failed, to the speed of rotation of the other engine of the aircraft (or of another engine of the aircraft when it comprises more than two engines).
Thus, by virtue of the invention, should there be a fault with the main regulating system, the means of supply of the corresponding auxiliary regulating system is controlled automatically so as to regulate the power of the associated engine, thereby decreasing the workload of the pilot since the latter no longer needs to adjust the fuel flow rate manually. Additionally, by virtue thereof, it is not necessary to provide specific training for the pilot.
Furthermore, as will be seen in greater detail hereinbelow, the regulating device in accordance with the invention is especially simple and robust, and inexpensive.
In a preferred embodiment, at least one of said supply means comprises an electric actuator, which comprises for example a DC motor or a stepper motor, and a fuel metering valve.
Advantageously, said fuel metering valve comprises an anti-shutdown stop of standard type. This makes it possible to decelerate the engine without risk of shutdown. It is conceivable to envisage one and the same metering valve for the main regulating system and the auxiliary regulating system which are associated with one and the same engine.
Within the framework of the present invention, each of said triggering means is:
either manual (on switch), so that an action from the pilot is required in case of a failure, but only in order to trigger the auxiliary regulating system, the control of the flow rate being achieved automatically of course when said auxiliary regulating system (or backup system) is triggered;
or automatic. This avoids the need for the pilot to release the controls in order to switch on the auxiliary regulating system. If all the triggering means are automatic, the power regulating device in accordance with the invention comprises no manual control.
Moreover, advantageously, at least one of said auxiliary regulating systems furthermore comprises a display means capable of depicting on a display screen the state of said auxiliary regulating system.
The present invention also relates to a process for regulating the power of the engines of a rotary wing aircraft, in particular a helicopter which is furnished with at least two engines, each of which comprises a main regulating system.
This regulating process is noteworthy, according to the invention, in that when one of said main regulating systems has failed, the flow rate of fuel which is fed to the engine, whose main regulating system has failed, is controlled automatically by way of an auxiliary regulating system in such a way as to slave the speed of rotation NG1 of this engine to the speed of rotation NG2 of the other engine (whose main regulating system has not failed).
Advantageously, the flow rate of fuel is controlled in such a way that the increase or the decrease in said flow rate is variable and varies as a function of the discrepancy between the speed of rotation NG1 and the speed of rotation NG2. This enables the following twofold objective to be satisfied
slow increasing or decreasing of the fuel flow rate near the preset range, so as to ensure the stability of the auxiliary regulating system with regard to slight disturbances; and
fast increasing or decreasing of the fuel flow rate far from the preset range.
In a preferred embodiment, to slave the speed of rotation NG1 to the speed of rotation NG2:
the following expression E is determined:
E=NG1+K.dNG1/dt
xe2x80x83in which:
K is a predetermined parameter; and
dNG1/dt is the derivative with respect to time of the speed of rotation NG1;
this expression E is compared with thresholds which are defined on the basis of the speed of rotation NG2; and
the slaving to be carried out is deduced on the basis of this comparison.
The introduction of a differentiation parameter dNG1/dt makes it possible to ensure anticipation with regard to the crossing of the thresholds by the speed NG1. Moreover, the order delivered is clipped so as to guarantee that the engine controlled by the auxiliary regulating system is maintained within a normal operating range in flight.
Additionally, in a variant embodiment, the fuel flow rate is controlled as follows:
in a case a), for which the following conditions hold simultaneously:
NG2 greater than 60% and NG1 greater than 75%,
xcex94=(|NG2xe2x88x92NG1|+0.9d|NG2xe2x88x92NG1|/dt) greater than 1%
xe2x80x83d/dt being the derivative with respect to time, and
(NG2xe2x88x92NG1) less than 0,
xe2x80x83the fuel flow rate is reduced;
in a case b), for which the following conditions hold simultaneously:
NG2 greater than 70% and NG1 greater than 75%,
xcex94=(|NG2xe2x88x92NG1|+0.9d|NG2xe2x88x92NG1|/dt) greater than 1%, and
(NG2xe2x88x92NG1) greater than 0,
xe2x80x83the fuel flow rate is increased; and
otherwise, in a case c), the fuel flow rate is maintained at the value which it had upon the appearance of said failure.
In this variant embodiment, preferably, the fuel flow rate is controlled by controlling the speed of rotation of an electric actuator which is associated with a fuel metering valve and, for case a), in order to reduce the fuel flow rate, a speed of rotation of the electric actuator of substantially 9xc2x0/s is ordered if the discrepancy xcex94 is greater than 3% and a speed of rotation of the electric actuator of substantially 3xc2x0/s is ordered if the discrepancy xcex94 is less than or equal to 3%, and for case b) in order to increase the fuel flow rate, a speed of rotation of the electric actuator of substantially 3xc2x0/s is ordered.
Furthermore, more especially although not exclusively, said fuel metering valve is common to a main regulating system and an auxiliary regulating system which are associated.